Experimental and numerical study on the explosion suppression of hydrogen/dimethyl ether/methane/air mixtures by water mist containing NaHCO3

Abstract

The explosion suppression effect of NaHCO3 water mist on the H2/DME/CH4/air mixtures was experimentally investigated. Pressure data and flame images were recorded by a pressure sensor and a high-speed camera, respectively. The suppression mechanism of NaHCO3 water mist was further studied using a developed kinetic model. Results showed that the normalized laminar flame speed calculated by kinetic model agreed well with the experimental data. The suppression effect of NaHCO3 water mist on the H2/DME/CH4/air mixtures explosion was significantly affected by fuel compositions, equivalence ratios and NaHCO3 concentrations. For stoichiometric mixtures (Φ = 1.0), the decreasing rate of the average flame propagation speed of CH4-enriched flames can be up to 84.9%, which is higher than that of DME-enriched flames and the H2-enriched flames. For DME-enriched flames, the decreasing rate of the average flame propagation speed of fuel-lean flames can also be up to 70%. Meanwhile, the maximum explosion pressure of the CH4-enriched flames and fuel-lean flames are more sensitive to the NaHCO3 water mist. The NaHCO3 water mist can suppress hydrodynamic instability while it has little effect on diffusional-thermal instability. The chemical kinetic model revealed that both the adiabatic flame temperature and the maximum mole fraction of (H + OH) can be decreased noticeably by NaHCO3 water mist. Sensitivity analysis indicated that NaOH + H = Na + H2O and Na + OH + M = NaOH + M are the dominant reactions of sodium-containing species for suppressing laminar flame speed. Reaction pathway analysis indicated that Na <=> NaOH suppression cycle is effective to reduce H and OH free radicals.